Mildred Cohn pioneered the use of stable isotopic tracers to study the mechanisms of enzymes and did critical work in nuclear magnetic resonance.

Mildred Cohn pioneered the use of stable isotopic tracers to study the mechanisms of enzymes and did critical work in nuclear magnetic resonance. (University of Pennsylvania)

Thomas H. Maugh II

Mildred Cohn, a chemist who overcame both religious and sexual prejudice to make major contributions in applying physics to problems of biology, died of respiratory failure Oct. 12 at Penn Presbyterian Medical Center in Philadelphia. She was 96.

Refusing to accept the limitations imposed on her by others, Cohn worked with four Nobel laureates over the course of her career, eventually earning the nation's highest science award, the National Medal of Science, in her own right.

Cohn pioneered the use of stable isotopic tracers to study the mechanisms of enzymes, which are the proteins that carry out chemical reactions within the cell. Stable isotopes, such as carbon-13 and oxygen-18, have the same chemical properties as their more common sisters -- in this case, carbon-12 and oxygen-16 -- but they do not disintegrate radioactively. When stable isotopes are incorporated into molecules in the cell, their heavier weight allows them to be traced, providing insights into biochemical reactions.

Cohn also did critical work in nuclear magnetic resonance (NMR), an imaging technique that allows chemists to examine the structure of proteins and other molecules in solution. Her early studies illuminated the role of adenosine triphosphate, or ATP, one of the crucial energy sources within the cell. Over her career, she published more than 160 papers, many of them seminal in her field.

Mildred Cohn was born in New York City on July 12, 1913, the daughter of Russian immigrants. Her father, who had trained as a rabbi in Russia but who worked in the garment and printing industries in New York, encouraged her ambitions, warning her that she would have to make extra effort to succeed.

She graduated from high school at 14 and enrolled at Hunter College, where her ambition was to study physics. The college did not offer a physics major, however, so she settled for chemistry. Even then, her instructor warned her that he could prepare her only to teach chemistry because working in a laboratory was not "ladylike." She received her bachelor's degree in three years, at age 17.

Cohn enrolled in the doctoral program at Columbia but could not get support as a teaching assistant because such jobs were reserved for men. She supported herself as a baby sitter, receiving a master's in physical chemistry in 1932. Unable to afford to continue her education, she accepted a job at the National Advisory Committee for Aeronautics, the forerunner of NASA, in Langley, Va., where she was the only female among 70 men.

She was given a position lower than she was qualified for and was eventually banned from the laboratory because she was a woman, but she planned fuel-injection experiments that others carried out.

After saving up her money, she returned to Columbia, where she worked with eventual Nobel laureate Harold Urey using isotopes to study reaction mechanisms. She received her doctorate in 1937 but had difficulty finding a job. Recruiters were seeking "PhD candidates, male and Christian."

She accepted a postdoctoral position with another Nobel laureate-to-be, biochemist Vincent du Vigneaud of George Washington University Medical School, where she used stable isotopes to study the metabolism of sulfur-containing amino acids. While there, she met physicist Henry Primakoff, whom she married in 1938. She did not change her name because, with war imminent, she wanted to advertise her heritage.

During the war, Cohn and draft-exempt men continued their research in Urey's lab, while he and others supported the war effort. In 1946, Primakoff accepted a position at Washington University in St. Louis and Cohn got a job as a research assistant in the laboratory of Nobel laureates Gerti T. Cori and Carl F. Cori, where she used a heavy isotope of oxygen to study the reactions of organic phosphate. She also initiated her studies of NMR there.

Two years later, Primakoff became a professor at the University of Pennsylvania, and Cohn accepted an assistant professorship in the chemistry department, becoming a full professor a year later. She retired in 1985, but retained an office on campus and was still active in research.

In 1964, she became the only woman to receive the American Heart Assn.'s Lifetime Career Award, which provided funding until she turned 65. She was the first woman on the editorial board of the prestigious Journal of Biological Chemistry and was editor for 10 years. In 1983, President Reagan honored her with the National Medal of Science. She was inducted into the National Women's Hall of Fame the day after she died.

Primakoff died in 1983. Cohn is survived by two daughters, Nina Rossomando and Laura Primakoff; a son, Paul Primakoff; six grandchildren; and four great-grandchildren.